Hybrid fibroin-nanocellulose composites for the consolidation of aged and historical silk

Silk artifacts are a valuable artistic and historical heritage, but are prone to degradation that makes the fibers fragile, hindering the preservation of precious collections. Dispersions of self-regenerated silk fibroin (SRSF) can be used to cast films on aged fibers and recover their mechanical properties, but there appears to be a limit to the fibroin concentration in the dispersions, as too concentrated systems produce highly crystalline but mechanically brittle films. Alternatively, we propose here hybrid dispersions of SRSF and cellulose nanocrystals (CNC) with the aim to grant the aged fibers improved strength, taking advantage of the SRSF structuration induced by CNC, and of the intrinsic mechanical properties of the cellulose crystals. We demonstrate that CNC speeds up the assembly of fibroin in the hybrid dispersions, leading to the formation of more compact colloidal structures at the nanoscale than the sole SRSF. When the hybrid dispersions film, the presence of CNC favors the formation of crystalline structures (most notably α-helices) even at low fibroin concentration, and the films confer optimal axial strength to aged silk fibers, surpassing the performance of single-component (SRSF or CNC) dispersions at the same concentration of consolidant, and of pure crystalline SRSF. Overall, the hybrid formulations candidate as new sustainable tools for the preservation of historical textiles, employing renewable materials (cellulose and silk scraps) to restore artifacts.